This is my small Christmas present for those who like zero NFB single-ended class A amplification

I've worked in my spare time (for last year and half) on a home project to make a very linear single-ended transistor amplifier without NFB and one of my ideas I've described in a small article on my web site here:

The performance of this circuit, despite the simplicity of the concept, is quite impressive - here is one example:

For a voltage amplifier stage using this idea I've measured distortion levels vs RMS current in the load resistor. Idle DC current was 4.5 mA, for 0.15 mA RMS current THD were 0.0025%, for 0.5 mA - 0.03%, for 1.15mA RMS (that is a swing from 3 to 6 mA (!) ) - only 0.16% .

It is possible to make this approach work even without the source resistor, thought it requires very careful transistors selection. THe circuit of my headphone amplifier (A.N.T. Audio "Amber") includes a voltage amplifier stage based on this idea.

Very interesting indeed. To avoid opamps some I/V converters for DACS use valves. They rely on something like a 50 ohm resistor to ground followed by a valve voltage amplification stage. Would you say this topology is suitable for this purpose? That would be great, because few CD players have space for valve stages.

Originally posted by Hennie Very interesting indeed. To avoid opamps some I/V converters for DACS use valves. They rely on something like a 50 ohm resistor to ground followed by a valve voltage amplification stage. Would you say this topology is suitable for this purpose? That would be great, because few CD players have space for valve stages.

This topology can be used in many applications, including this one . For 50 Ohm and, say, FS 1 mA RMS output current of the DAC, the maximum input voltage would be 50 mV - near the "sweet spot" for this circuit, with a possibility of a very decent performance - with the distortions about 0.002% (mostly 2-nd order) and SNR about 100 dB.